kernel: restore compat code required for old kernels

This commit restores compatibility code needed that was removed at tiann/KernelSU@898e9d4 .
where upstream dropped all pre-5.10 support

Reverts `kernel:Add Huawei hisi check (tiann#1545)`
	- upstream tiann/KernelSU@4f05fe2
	- superceded by `kernel: expose allowlist workaround as Kconfig option`
Reverts `throne_tracker: avoid cross fs access (tiann#2626)`
	- upstream tiann/KernelSU@0b6998b
	- superceded by `throne_tracker: avoid cross-fs traversal using s_magic check`

other changes and cleanups
	sucompat: ksu_handle_stat(), remove dead ifdef.
		- just use `ksu_handle_stat(&dfd, &filename->name, &flags);` if you want to hook vfs_statx on 6.1
	LINUX_VERSION_CODE / KERNEL_VERSION, ksu.c
		- reported by Sinclair19
		- fix by including version.h
	fatal_signal_pending, ksud.c
		- add compat by including sched.h or sched/signal.h conditionally
		- ref: torvalds/linux@2a1f062

Signed-off-by: backslashxx <[email protected]>

Author: backslashxx

kernel/Makefile

@@ -29,6 +29,14 @@ $(warning "KSU_GIT_VERSION not defined! It is better to make KernelSU a git subm
 ccflags-y += -DKSU_VERSION=16
 endif
 
+ifeq ($(shell grep -q " current_sid(void)" $(srctree)/security/selinux/include/objsec.h; echo $$?),0)
+ccflags-y += -DKSU_COMPAT_HAS_CURRENT_SID
+endif
+
+ifeq ($(shell grep -q "struct selinux_state " $(srctree)/security/selinux/include/security.h; echo $$?),0)
+ccflags-y += -DKSU_COMPAT_HAS_SELINUX_STATE
+endif
+
 ifndef KSU_EXPECTED_SIZE
 KSU_EXPECTED_SIZE := 0x033b
 endif
@@ -48,6 +56,13 @@ $(info -- KernelSU Manager signature hash: $(KSU_EXPECTED_HASH))
 ccflags-y += -DEXPECTED_SIZE=$(KSU_EXPECTED_SIZE)
 ccflags-y += -DEXPECTED_HASH=\"$(KSU_EXPECTED_HASH)\"
 
+ifeq ($(shell grep -q "int path_umount" $(srctree)/fs/namespace.c; echo $$?),0)
+ccflags-y += -DKSU_UMOUNT
+else
+$(info -- Did you know you can backport path_umount to fs/namespace.c from 5.9?)
+$(info -- Read: https://kernelsu.org/guide/how-to-integrate-for-non-gki.html#how-to-backport-path-umount)
+endif
+
 ccflags-y += -Wno-implicit-function-declaration -Wno-strict-prototypes -Wno-int-conversion -Wno-gcc-compat
 ccflags-y += -Wno-declaration-after-statement -Wno-unused-function
 

kernel/allowlist.c

@@ -8,7 +8,9 @@
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/version.h>
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0)
 #include <linux/compiler_types.h>
+#endif
 
 #include "ksu.h"
 #include "klog.h" // IWYU pragma: keep

kernel/core_hook.c

@@ -18,7 +18,6 @@
 #include <linux/namei.h>
 
 #include "allowlist.h"
-
 #include "core_hook.h"
 #include "klog.h" // IWYU pragma: keep
 #include "ksu.h"
@@ -87,7 +86,11 @@ static void setup_groups(struct root_profile *profile, struct cred *cred)
 			put_group_info(group_info);
 			return;
 		}
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 9, 0)
 		group_info->gid[i] = kgid;
+#else
+		GROUP_AT(group_info, i) = kgid;
+#endif
 	}
 
 	groups_sort(group_info);
@@ -605,7 +608,23 @@ static int ksu_task_prctl(int option, unsigned long arg2, unsigned long arg3,
 	ksu_handle_prctl(option, arg2, arg3, arg4, arg5);
 	return -ENOSYS;
 }
-
+// kernel 4.4 and 4.9
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+static int ksu_key_permission(key_ref_t key_ref, const struct cred *cred,
+			      unsigned perm)
+{
+	if (init_session_keyring != NULL) {
+		return 0;
+	}
+	if (strcmp(current->comm, "init")) {
+		// we are only interested in `init` process
+		return 0;
+	}
+	init_session_keyring = cred->session_keyring;
+	pr_info("kernel_compat: got init_session_keyring\n");
+	return 0;
+}
+#endif
 static int ksu_inode_rename(struct inode *old_inode, struct dentry *old_dentry,
 			    struct inode *new_inode, struct dentry *new_dentry)
 {
@@ -622,11 +641,19 @@ static struct security_hook_list ksu_hooks[] = {
 	LSM_HOOK_INIT(task_prctl, ksu_task_prctl),
 	LSM_HOOK_INIT(inode_rename, ksu_inode_rename),
 	LSM_HOOK_INIT(task_fix_setuid, ksu_task_fix_setuid),
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+	LSM_HOOK_INIT(key_permission, ksu_key_permission)
+#endif
 };
 
 void __init ksu_lsm_hook_init(void)
 {
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 11, 0)
 	security_add_hooks(ksu_hooks, ARRAY_SIZE(ksu_hooks), "ksu");
+#else
+	// https://elixir.bootlin.com/linux/v4.10.17/source/include/linux/lsm_hooks.h#L1892
+	security_add_hooks(ksu_hooks, ARRAY_SIZE(ksu_hooks));
+#endif
 }
 
 void __init ksu_core_init(void)

kernel/kernel_compat.c

@@ -1,10 +1,38 @@
 #include <linux/version.h>
 #include <linux/fs.h>
 #include <linux/nsproxy.h>
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 10, 0)
 #include <linux/sched/task.h>
+#else
+#include <linux/sched.h>
+#endif
 #include <linux/uaccess.h>
 #include "klog.h" // IWYU pragma: keep
-#include "kernel_compat.h"
+
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+#include "linux/key.h"
+#include "linux/errno.h"
+#include "linux/cred.h"
+struct key *init_session_keyring = NULL;
+
+static inline int install_session_keyring(struct key *keyring)
+{
+	struct cred *new;
+	int ret;
+
+	new = prepare_creds();
+	if (!new)
+		return -ENOMEM;
+
+	ret = install_session_keyring_to_cred(new, keyring);
+	if (ret < 0) {
+		abort_creds(new);
+		return ret;
+	}
+
+	return commit_creds(new);
+}
+#endif
 
 extern struct task_struct init_task;
 
@@ -50,6 +78,13 @@ void ksu_android_ns_fs_check()
 
 struct file *ksu_filp_open_compat(const char *filename, int flags, umode_t mode)
 {
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+	if (init_session_keyring != NULL && !current_cred()->session_keyring &&
+	    (current->flags & PF_WQ_WORKER)) {
+		pr_info("installing init session keyring for older kernel\n");
+		install_session_keyring(init_session_keyring);
+	}
+#endif
 	// switch mnt_ns even if current is not wq_worker, to ensure what we open is the correct file in android mnt_ns, rather than user created mnt_ns
 	struct ksu_ns_fs_saved saved;
 	if (android_context_saved_enabled) {
@@ -72,17 +107,69 @@ struct file *ksu_filp_open_compat(const char *filename, int flags, umode_t mode)
 ssize_t ksu_kernel_read_compat(struct file *p, void *buf, size_t count,
 			       loff_t *pos)
 {
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0)
 	return kernel_read(p, buf, count, pos);
+#else
+	loff_t offset = pos ? *pos : 0;
+	ssize_t result = kernel_read(p, offset, (char *)buf, count);
+	if (pos && result > 0) {
+		*pos = offset + result;
+	}
+	return result;
+#endif
 }
 
 ssize_t ksu_kernel_write_compat(struct file *p, const void *buf, size_t count,
 				loff_t *pos)
 {
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0)
 	return kernel_write(p, buf, count, pos);
+#else
+	loff_t offset = pos ? *pos : 0;
+	ssize_t result = kernel_write(p, buf, count, offset);
+	if (pos && result > 0) {
+		*pos = offset + result;
+	}
+	return result;
+#endif
 }
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 8, 0)
 long ksu_strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
 				   long count)
 {
 	return strncpy_from_user_nofault(dst, unsafe_addr, count);
 }
+#elif LINUX_VERSION_CODE >= KERNEL_VERSION(5, 3, 0)
+long ksu_strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
+				   long count)
+{
+	return strncpy_from_unsafe_user(dst, unsafe_addr, count);
+}
+#else
+// Copied from: https://elixir.bootlin.com/linux/v4.9.337/source/mm/maccess.c#L201
+long ksu_strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
+				   long count)
+{
+	mm_segment_t old_fs = get_fs();
+	long ret;
+
+	if (unlikely(count <= 0))
+		return 0;
+
+	set_fs(USER_DS);
+	pagefault_disable();
+	ret = strncpy_from_user(dst, unsafe_addr, count);
+	pagefault_enable();
+	set_fs(old_fs);
+
+	if (ret >= count) {
+		ret = count;
+		dst[ret - 1] = '\0';
+	} else if (ret > 0) {
+		ret++;
+	}
+
+	return ret;
+}
+#endif

kernel/kernel_compat.h

@@ -1,29 +1,19 @@
 #ifndef __KSU_H_KERNEL_COMPAT
 #define __KSU_H_KERNEL_COMPAT
 
-#include <linux/fs.h>
-#include <linux/version.h>
-#include "ss/policydb.h"
+#include "linux/fs.h"
+#include "linux/key.h"
+#include "linux/version.h"
 #include "linux/key.h"
-
-/*
- * Adapt to Huawei HISI kernel without affecting other kernels ,
- * Huawei Hisi Kernel EBITMAP Enable or Disable Flag ,
- * From ss/ebitmap.h
- */
-#if (LINUX_VERSION_CODE >= KERNEL_VERSION(4, 9, 0)) &&                           \
-		(LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)) ||               \
-	(LINUX_VERSION_CODE >= KERNEL_VERSION(4, 14, 0)) &&                      \
-		(LINUX_VERSION_CODE < KERNEL_VERSION(4, 15, 0))
-#ifdef HISI_SELINUX_EBITMAP_RO
-#define CONFIG_IS_HW_HISI
-#endif
-#endif
 
 extern long ksu_strncpy_from_user_nofault(char *dst,
 					  const void __user *unsafe_addr,
 					  long count);
 
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 10, 0)
+extern struct key *init_session_keyring;
+#endif
+
 extern void ksu_android_ns_fs_check();
 extern struct file *ksu_filp_open_compat(const char *filename, int flags,
 					 umode_t mode);

kernel/ksu.c

@@ -2,6 +2,7 @@
 #include <linux/fs.h>
 #include <linux/kobject.h>
 #include <linux/module.h>
+#include <linux/version.h> /* LINUX_VERSION_CODE, KERNEL_VERSION macros */
 #include <linux/workqueue.h>
 
 #include "allowlist.h"
@@ -70,4 +71,7 @@ module_exit(kernelsu_exit);
 MODULE_LICENSE("GPL");
 MODULE_AUTHOR("weishu");
 MODULE_DESCRIPTION("Android KernelSU");
+
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 0, 0)
 MODULE_IMPORT_NS(VFS_internal_I_am_really_a_filesystem_and_am_NOT_a_driver);
+#endif

kernel/ksud.c

@@ -6,12 +6,23 @@
 #include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/version.h>
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 4, 0)
 #include <linux/input-event-codes.h>
+#else
+#include <uapi/linux/input.h>
+#endif
+#if LINUX_VERSION_CODE < KERNEL_VERSION(4, 1, 0)
+#include <linux/aio.h>
+#endif
 #include <linux/printk.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
 #include <linux/workqueue.h>
-#include <linux/sched/signal.h>
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(4, 11, 0)
+#include <linux/sched/signal.h> /* fatal_signal_pending */
+#else
+#include <linux/sched.h> /* fatal_signal_pending */
+#endif
 
 #include "allowlist.h"
 #include "klog.h" // IWYU pragma: keep
@@ -143,7 +154,6 @@ int ksu_handle_execveat_ksud(int *fd, struct filename **filename_ptr,
 			     struct user_arg_ptr *argv,
 			     struct user_arg_ptr *envp, int *flags)
 {
-
 	if (!ksu_execveat_hook) {
 		return 0;
 	}
@@ -341,7 +351,7 @@ int ksu_handle_vfs_read(struct file **file_ptr, char __user **buf_ptr,
 	// we only process the first read
 	static bool rc_inserted = false;
 	if (rc_inserted) {
-		// we don't need this kprobe, unregister it!
+		// we don't need this hook, unregister it!
 		stop_vfs_read_hook();
 		return 0;
 	}
@@ -412,7 +422,6 @@ static bool is_volumedown_enough(unsigned int count)
 int ksu_handle_input_handle_event(unsigned int *type, unsigned int *code,
 				  int *value)
 {
-
 	if (!ksu_input_hook) {
 		return 0;
 	}

kernel/selinux/rules.c

@@ -9,7 +9,9 @@
 #include "linux/lsm_audit.h"
 #include "xfrm.h"
 
+#if LINUX_VERSION_CODE >= KERNEL_VERSION(5, 10, 0)
 #define SELINUX_POLICY_INSTEAD_SELINUX_SS
+#endif
 
 #define KERNEL_SU_DOMAIN "su"
 #define KERNEL_SU_FILE "ksu_file"
@@ -19,8 +21,18 @@
 static struct policydb *get_policydb(void)
 {
 	struct policydb *db;
+// selinux_state does not exists before 4.19
+#ifdef KSU_COMPAT_USE_SELINUX_STATE
+#ifdef SELINUX_POLICY_INSTEAD_SELINUX_SS
 	struct selinux_policy *policy = rcu_dereference(selinux_state.policy);
 	db = &policy->policydb;
+#else
+	struct selinux_ss *ss = rcu_dereference(selinux_state.ss);
+	db = &ss->policydb;
+#endif
+#else
+	db = &policydb;
+#endif
 	return db;
 }
 
@@ -169,7 +181,8 @@ static int get_object(char *buf, char __user *user_object, size_t buf_sz,
 // reset avc cache table, otherwise the new rules will not take effect if already denied
 static void reset_avc_cache()
 {
-#if (LINUX_VERSION_CODE >= KERNEL_VERSION(6, 4, 0))
+#if ((!defined(KSU_COMPAT_USE_SELINUX_STATE)) || \
+        LINUX_VERSION_CODE >= KERNEL_VERSION(6, 4, 0))
 	avc_ss_reset(0);
 	selnl_notify_policyload(0);
 	selinux_status_update_policyload(0);